Optical Properties of Tigernut (Cyperus Esculentus) Asinfluenced by Moisture Content and Wavelength

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Abstract
Tigernut (cyperusesculentus) is one among the underutilized
crops in Nigeria despite its high economic value. This study
investigated the absorbance, transmittance and colour of yellow
tigernut as influenced by moisture content at 8%, 16%, 24%, 32%
and 42% (db) respectively. The tigernut samples were collected
directly from a farm in Minna, Niger state and cleaned to remove
all foreign materials, initial moisture content was determined
using ASAE standard after which sampleswere conditioned to the
desired moisture levels following standard method. Using a
spectrophotometer, the absorbance ranged from 3.04 to 6.35 and
transmittance ranged from 0.00 to 0.19 within a wavelength range
of 320nm to 720nm while the colour using a Chroma meter
ranged from 3.73 to 4.14, 5.19 to 8.18 and 13.1 to 19.0 for L
(brightness), a (red) and b (yellow) respectively. ANOVA also
revealed that moisture has significant effect at p<0.05 on
absorbance, transmittance and colour of the tigernut. Correlation
and regression analysis revealed a positive linear relationship
between all moisture contents with absorbance, transmittance and
colour.
Keywords
Moisture content, optical properties, absorbance, transmittance,
colour and tigernut
1. Introduction
Tigernut (CyperusEsculentus) is a perennial grass-like plant that
is cultivated between March and December in Nigeria with
spherical tubers of dimension 8mm-16mm as reported by Osagie
et al. [1]. It is a pale yellow cream kernel surrounded by a fibrous
sheath that have been cultivated for over 400 years ago in both
commercial and substantial quantity depending on its demand.
According to Obadina et al. [2] tigernut generally is called earth
almonds but different people from different countries have
different names for tigernut.
In Nigeria, Tigernut is call aya by the Hausa’s, akiawusaby the
Igbo’s and ofioby the Yoruba’s. It is cultivated more in the middle
belt and northern regions of Nigeria. Tigernut has three varieties
classified based on colour, which are Black, Brown and Yellow
varieties [3]. According to Okafor et al. [4] and Ebringa [5], the
yellow variety is considered the best among the three varieties
because of its large size; the fact that more milk can be extracted
from it when processed, contains higher protein, has lower fat
content and less anti nutritional factors such as polyphenol.
Until recently, there was dearth of information about the
potential health benefits of this ancient food tigernut in Nigeria
[6]. Tigernuts are edible, sweet, nutty, flavoured tubers that
contain protein, carbohydrate, sugars, and lots of oil and fiber [7].
It can be processed into many other edible products. According
to Gambo and Da’u [7], tiger nut is one among the best nutritional
crops used to augment the diet of humans. Tigernut can be
roasted, dried, baked and made into milk recommended for those
who have heavy digestion, diarrhea and dysentery because of its
high content of digestive enzymes and no lactose or gluten
content [8].
Tigernut has 30% of non drying oil which when extracted is
cholesterol free and has very low sodium content. It has a
composition similar to olive oil and rich mineral contents such as
potassium and phosphorus. Tigernut tuber has very high fiber
content that makes it very healthy and does not lose its nutritional
contents during milling process as reported by Salau et al. [9].
Bamishaiye and Bamishaiye [6] reported that tigernut is an
excellent source of minerals such as iron and calcium that are
essential for body growth and development. He continues by
saying tiger nut can help to prevent heart attacks, thrombosis and
activate blood circulation and due to the high contents of soluble
glucose, it can help prevent cancer and reduce the risk of suffering
colon cancer.
Despite these numerous importance of tigernut as a
multipurpose tuber, it has been one among the neglected and
underutilized crops in Nigeria because of inadequate knowledge
on its production, utilization, nutritional and health value, and
non-availability of processing machines as reported by
Bamishaiye and Bamishaiye [6].
Tigernut is locally processed without minding the effect on its
nutritional quality or value. Developing mechanized processes
for harvesting, cleaning, drying, oil or milk extraction, handling
and storage facilities for tigernut cannot be successful without an
accurate knowledge and availability of itsengineering
propertiessuch as physical, mechanical, thermal, optical, electrical
properties among others. Studies carried out are majorly on
physical properties of tigernut but little has been reported on its
mechanical properties while none has been reported for optical
19
HUNGARIAN AGRICULTURAL ENGINEERING
N° 34/2018 19-23
Published online: http://hae-journals.org/
HU ISSN 0864-7410 (Print) / HU ISSN 2415-9751(Online)
DOI: 10.17676/HAE.2018.34.19
Research Article
OPTICAL PROPERTIES OF TIGERNUT (CYPERUS ESCULENTUS) AS
INFLUENCED BY MOISTURE CONTENT AND WAVELENGTH
Author(s):
P. A. Omale1– M. O. Omobowale1– B. N. Iyidiobu2
Affiliation:
1Department of Agricultural and Environmental Engineering, University of Agriculture, Makurdi, Benue state
2Department of Agricultural Engineering, Faculty of Technology, University of Ibadan, Ibadan, Oyo state
Email address:
ayeslody4all@gmail.com, yimikaomo@yahoo.co.uk, zikalike@gmail.com
PERIODICAL OF THE COMITTEE OF
AGRICULTURAL AND BIOSYSTEM
ENGINEERING OF
THE HUNGARIAN ACADEMY OF SCIENCES
and
SZENT ISTVÁN UNIVERSITY
Faculty of Mechanical Engineering
Received: 2018.10.03.; Accepted: 2018.12.11.

properties. The optical properties are needed in the designing of
machines for unit process operations such as sorting, cleaning and
grading of tigernut that will monitor and control the quality
activities of the tuber and saves human time and labour.
The objective of this study is to determine the absorbance,
transmittance and colour of tigernut as influenced by moisture
content and wavelength.
2. Materials and Methods
Sample Preparation and Conditioning
The yellow variety of tigernut was purchased from a farm located
in Minna Local Government Area of Niger State, Nigeria
immediately after harvest and were cleaned and sorted manually
and all foreign matter (such as dirt, stones, premature and broken
seeds) were removed and stored in a plastic container. The initial
moisture contents of the samples was determined to be 7.8%db
using the ASAE standard [10] by oven drying the sample at
103°C for 48 hours at the multipurpose central laboratory,
university of Ibadan
The sample was divided into five equal weights and
conditioned to the desired moisture contents of 8%, 16%, 24%,
32% and 40% (db) each by weighing and adding a calculated
amount of distilled water using the Equation 1 below.
Where; Q is the mass of water to be added in kg, is the initial
mass of the sample in kg, is the initial moisture content of the
sample in % d.b and is the final moisture content in % d.b
The conditioned samples were stored in airtight polythene and
kept in a refrigerator at 5°C for 168 hours (7 days) to ensure
uniformity of distributed moisture throughout the samples. The
moisture content of the conditioned samples was verified after
the seventh day before being used for determining the absorbance,
transmittance and colourof the samples.
Determination of Transmittance and Absorbance
A Jenway 6850UV/Vis Spectrophotometer at the food science
and technology laboratory, University of Ibadan, was used to
determine the transmittance and absorbance of the tuber at
various moisture contents with variation of wavelengths within
visible light spectra range of 320nm, 420nm, 520nm, 620nm and
720 nm.
Transmittance and absorbance were read directly from the
spectrophotometer digital display at different wavelength. The
machine was switched on and allowed to warm for 15 minutes
after which the sample cell was filled with water and placed inside
the cell holder. The blank button was pressed to have zero
Absorbance and Transmittance. The sample cell with water was
replaced with sample cell filled with samples in the machine. The
enter key was pressed to have the absorbance or transmittance
value in percentage. The readings were taken in five replicates.
Colour Measurement
Konica Minolta Chroma meter CR-410 was used to give an
indicator of colour in the form of L,a,b colour solid values. The
L value is an indication of brightness and can be compared to the
reflectance information. The amount of red and
greenwasindicated by a positive or negative a value, respectively.
Similarly, the b value indicates the yellow and bluecolour in the
sample with its respective positive or negative number [11]. The
readings were taken in five replications.
3. Results and Discussion
Absorbance and Transmittance
The mean values of the absorbance and transmittance are
presented on Table 1 and it shows that the absorbance ranged
from 3.04 to 6.35 while the transmittance ranged from 0.00 to
0.19.
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(1)
Table 1. Mean Values of Absorbance and Transmittance of Yellow Tigernut as Influenced
by Moisture Content and Wave Length

The absorbance increased as moisture content increases (Figure
1) but decreased as the wavelength increases (Figure 2) within
constant moisture content.ANOVA revealed a significant
difference at P<0.05 among the absorbance of the yellow tigernut
at different moisture content (Table 2). This result is in line with
the reports of Hernandez et al. [12], Fang et al. [13] and Cubeddu
et al. [14] in their studies. Absorbanceis the capacity of a
substance to absorb light of a specified wavelength. This indicates
that the more the water content of tigernut, the more it will absorb
light rays and the higher the wavelength of the light ray, the lesser
the absorption capacity of tigernut.
Figure 1. Absorbance trend of tigernut influenced by moisture
Figure 2. Absorbance trend of tigernut
influenced by Wavelength
Figure 3. Transmittance trend of yellow tigernut
influenced by moisture
Transmittance of the yellow tigernut increased as both the
moisture content and wavelength increases(Figures 3 and 4).
ANOVA revealed a significant difference at P<0.05 among the
transmittance at different moisture content (Table 3). The result
is in line with those reported by El-Raieet al.,(2009) and Fang et
al. [13] in their research. Transmittance of the surface of a
material is its effectiveness in transmitting radiant energy. It is
the fraction of incident electromagnetic power transmitted
through a sample, in contrast to the transmission coefficient,
which is the ratio of the transmitted to the incident electric field.
Figure 4. Transmittance trend of yellow tigernut
influenced by WaveLength
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Table 2. ANOVA Result on absorbance of tigernut at 95% significant level
Correlation analysis performed on the Transmittance revealed
a stronger positive linear relationship of moisture and
wavelength with correlation coefficients(R) of .714 and .605
respectively.
Colour
The tigernut colour as influenced by moisture content was
measured using the KonicaMinolta Chroma meter and the mean

values presented on Table 5 revealed that the colour ranged from
3.73 to 4.14, 5.19 to 8.18 and 13.1 to 19.0for L (brightness), a
(red) and b (yellow) respectively. These values all increased as
the moisture content increases (Figures 5, 6 and 7).
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Table 3. ANOVA Result on transmittance of tigernut at 95% significant level
Table 4. Mean Values of Tigernut Colour as Influenced by Moisture Content
Table 5: ANOVA Result on colour of tigernut at 95% significant level
Figure 5: L (Brightness) trend
ANOVA, Regression and Correlation Analysis of colour
ANOVA revealed a significant difference at P<0.05 among the
L, a and b of the yellow tigernut at different moisture content
shown on table 4.Regression and correlation was carried out on
the L, a and b values and it revealed that there is a positive linear
relationship between moisture content and the L, a and b colour
values and the L, a and b as a function ofmoisture content can be
expressedusing the following linear regression equations;
L=36.231+1.080M with R=.796 and R²= .638
a=4.728+0.747M with R =.943 and R² =.890
b=11.342–.552M with R=.915 and R²=.837
Where L= Brightness, a=Red, b=Yellow and M=Moisture
content.
Figure 6: a(Red) trend

Figure 7: b(Yellow) trend
4. Conclusion
This study investigated the absorbance, transmittance and colour
of yellow tigernut (cyperus esculentus) as affected by moisture
content and based onthe results obtained,Moisture content and
wavelength have significant influence at P<0.05 on the
absorbance, transmittance and colour of yellow tigernut. The
moisture and wavelength has a poor positive linear relationship
with absorbance and a stronger positive linear relationship with
transmittance and colour (Lab).
References
[1] Osagie, A. U., Okoye, W. I., Oluwayose, B. O., Dawodu, O.
A.: 1986. Chemical quality parameters and fatty acid position of
oils of underexploited tropical seeds. Nigerian Journal of Applied
Science Vol. 4. pp. 151-162.
[2] Obadina, A. O., Oyawole, O. B., Ayoola, A. A.: 2008.
Quality assessment of Gari produced using rotary drier: In Food
Processing, Methods, Techniques and Trends. Edited by Valerie
C Bellinghouse.Nova Science Publishers.
[3] Osagie, A. U., Eka, S. A.: 1998. Lipid from plant source,
structure and distribution. Proceedings of the 1st Agricultural
Conference on Biochemistry of lipids, Vol. 103. pp. 21-26.
[4] Okafor, J. N. C., Mordi, J. I., Ozuma, A. U. Solomon, H.
M., Olatunji, O.: 2003. Preliminary studies on
thecharacteristics of contaminants in tigernuts (Yellow variety).
Proceeding of the 27th Annual Nigeria Institute of Food Science
and Technology (NIFST) conference, 13-17 October 2003, pp.
210-211.
[5] Ebringa, D. C.: 2007. Proximate Compositions of Peanut,
Tiger nut and walnut. In the Proceedings of NIFST 31st annual
conference/AGMAbuja, Nigeria. pp. 169-170.
[6] Bamishaiye, E. I., Bamishaiye, O .M.: 2011. Tiger Nut: as
a Plant, its derivatives and benefits. AJFAND African Journal of
Food, Agriculture, Nutrition and Development, Vol. 11 No. 5. pp.
5157-5170.
[7] Gambo, A., Da’u, A.: 2014. Tiger Nut (CyperusEsculentus):
Composition, Products, Uses and Health Benefits A Review.
Bayero Journal of Pure and Applied Sciences, Vol. 7. No. 1. pp.
56-61 http://dx.doi.org/10.4314/bajopas.v7i1.11
[8] Abaejoh, R., Djomdi, I., Ndojouenkeu, R.: 2006.
Characteristics of tigernut (Cyperus esculentus) tubers and their
performance in the production of a milky drink. Journal of Food
Processing Preservation, Vol. 30. No. 2. pp. 145-163.
http://dx.doi.org/10.1111/j.1745-4549.2006.00056.x
[9] Salau, R. B., Ndamitso M. M., Paiko, Y. B., Jacob, J. O.,
Jolayemi, O. O., Mustapha, S.: 2012. Assessment of the
proximate composition, food functionality and oil
characterization of mixed varieties of Cyperus esculentus (tiger
nut) rhizome flour. Continental J. Food Science and Technology,
Vol. 6. No. 2. pp. 13-19.
http://dx.doi.org/10.5707/cjfst.2012.6.2.13.19
[10] ASAE.: 1998. ASAE S352.2 Standards, 45th Ed , DEC. 97.
Moisture Measurement. Unground grain and seeds. America
Society of Agricultural Engineers, St. Joseph, Michigan, pp. 551.
[11] Mohsenin, N. N.: 1984. Electriomagnetic Radiation
Properties of foods and Agricultural Products. Gordon and Breach
Science Publishers, New York.
[12] Hernández, A. C., Domínguez-Pacheco, F. A., Cruz-Orea,
A., Herrera, C. A., Gutierrez, C. D., Zepeda, B. R., Ramírez,
M. E.: 2012. Optical absorption coefficient of different tortillas
by photoacoustic spectroscopy. African Journal of Biotechnology
Vol. 11. No. 92. pp. 15916-15922.
http://dx.doi.org/10.5897/AJB12.997
[13] Fang, Z. H., Fu, X. P., He, X. M.: 2016. Investigation of
absorption and scattering characteristics of kiwifruit tissue using
a single integrating sphere system. J Zhejiang Univ-Sci B.
(Biomed & Biotechnology), Vol. 17. No. 6. pp. 484-492.
http://dx.doi.org/10.1631/jzus.B1500086
[14] Cubeddu, R., Pifferi, A., Taroni P., Torricelli, A.: 2002.
Measuring fresh fruit and vegetable quality: advanced optical
methods. Section 8. Woodhead Publishing Ltd and CRC Press,
LLC.
[15] El-Raie, A. E., Hassan, H. E., Abd El-Rahman A. A.:
2009. Optical and Electrical Properties of Some Grains Using
Visible Laser. Misr J. Ag. Eng., Vol. 26. No. 3. pp. 1412- 1428.
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